’Speak unto the children of Israel, saying: If any man of you or of your generations shall be unclean by reason of a dead body, or be in a journey afar off, yet he shall keep the Passover unto the Lord;

in the second month on the fourteenth day at dusk they shall keep it; they shall eat it with unleavened bread and bitter herbs;

— Numbers 9:11

When it began:

Pesach Sheni began in the desert, during the first Passover holiday, and served as a "second chance" for those who were unable to offer the Passover sacrifice at the appropriate time due to ritual impurity. Today, we mark and commemorate the date by eating matzah (in the same way that we eat the afikoman - the matzah at the Passover seder in remembrance of the Passover offering.

How it’s observed today:

Today, Pesach Sheni on the 14th of Iyar has the status of a very minor holiday.

Customs:

There is a custom to eat a piece of kosher for Pesach matzah on the night of Pesach Sheni.